Air pollution

Types of air pollution

The most abundant and harmful pollutants include:

Particulate matter (PM)

What is it?

Particulate matter is a complex mixture of solids and liquids, including carbon, complex organic chemicals, sulphates, nitrates, mineral dust, and water suspended in the air.

It varies in size. Some particles, such as dust, soot, dirt or smoke are large or dark enough to be seen with the naked eye. But the most damaging particles are the smaller particles, known as PM10and PM2.5. PM10refers to particles with a diameter that’s smaller than 10 microns (10µm) – that’s 10 millionths of a metre. PM2.5 refers to particles with a diameter smaller than 2.5 microns, and these are known as fine particles. The smallest fine particles, less than 0.1 micron in diameter, are called ultrafine particles.

Diameters of particulate matter compared to a human hair

Where does it come from?

Man-made particulate matter mainly comes from industrial processes, construction work, emissions from diesel and petrol engines, friction from brakes and tyres, and dust from road surfaces. Diesel engines tend to produce much more than equivalent petrol engines.

Natural sources of particulate matter include volcanoes, sea spray, pollen and soil. It is also formed in the atmosphere when gases such as nitrogen dioxide and sulphur dioxide are changed in the air by chemical reactions.

How does it affect your lungs?

The size of particulate matter will determine where it will end up once you breathe it in. Larger particles may be trapped in your nose, while PM10 can reach your airways. Fine particles (PM2.5) may reach the breathing sacs deep in your lungs, and ultrafine particles may even cross into your blood stream. These particles can carry toxic chemicals which are linked to cancer.

Particulate matter irritates your nose and throat and may be associated with more severe symptoms in people with asthma. It results in more people with lung conditions (COPD, asthma, bronchitis) and heart conditions (heart attacks, strokes) being admitted to hospital. It also causes early deaths from lung and heart disease.

There’s also evidence that long-term exposure to particulate matter can contribute to the development of lung cancer and possibly asthma.

Nitrogen dioxide (NO2)

What is it?

Nitrogen dioxide is a gas and is a major component of urban air pollution episodes.

Where does it come from?

Man-made sources of nitrogen oxides, including nitrogen dioxide, are vehicles, power stations and heating. Diesel vehicles are major contributors in urban areas. Roadside levels are highest where traffic is busiest.

How does it affect your lungs?

High levels of NO2 can irritate and inflame the lining of your airways, causing a flare-up of asthma or COPD and symptoms such as coughing and difficulty breathing.

Children and older people are also more affected and more likely to develop a respiratory infection, or react to an allergen (any substance that triggers an allergic reaction, such as pollen).

Ozone (O3)

What is it?

Ozone is a gas composed of three atoms of oxygen. In the upper level of the Earth’s atmosphere, it absorbs harmful ultraviolet radiation.

Where does it come from?

Near the ground, ozone is made by a chemical reaction between the sun’s rays and organic gases and oxides of nitrogen emitted by cars, power plants, chemical plants and other sources.

Levels of ozone tend to be highest in the spring and summer and lowest in the winter. Ozone reaches its peak concentration during the afternoon. Levels are often higher in the country than in towns. Ozone is a major component of summer air pollution episodes.

How does it affect your lungs?

Ozone can irritate the airways of healthy people and people with lung conditions. High levels can cause you discomfort when you breathe, reduce your lung capacity (the amount of air your lungs can hold) and trigger asthma symptoms.

If you have a lung condition, high levels of ozone can cause you to have difficulty breathing, to wheeze and to cough. People with asthma may need to use their reliever inhaler more.

When there are high levels of ozone, more people are admitted to hospital with asthma-related health problems and COPD symptoms, and there is a greater risk of illnesses like pneumonia and bronchitis.

Sulphur dioxide (SO2)

What is it?

Sulphur dioxide is a colourless gas, with a pungent, suffocating smell. It’s produced by burning sulphur-containing fuels such as coal and oil. This includes, vehicles, power generation and heating.

Where does it come from?

Most sulphur dioxide comes from electric industries that burn fossil fuels, and also from petrol refineries and cement manufacturing. It can be transported over long distances and contributes to the formation of ozone.

How does it affect your lungs?

Sulphur dioxide can irritate the lining of your nose, throat and lungs. It can cause coughing and tightness of your chest, as well as a narrowing of your airway that will reduce the flow of air to your lungs. It inflames the airways, causing coughing and more mucus. It makes conditions like asthma and COPD worse. It makes people more prone to chest infections.

People with asthma are much more sensitive to sulphur dioxide than those who do not have asthma. They may find breathing more difficult and have flare-ups when concentrations of sulphur dioxide are high.

Next: The effects of air pollution >

If you have concerns or need advice, call our helpline on 03000 030 555 between 9am and 5pm on a weekday or email them.

We'll take good care of your personal info and you can update the way we contact you at any time - check out our privacy policy at to find out more.

Download our air pollution information (434KB, PDF)

Last medically reviewed: April 2017. Due for review: April 2020

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.